WASHINGTON (AP) — U.S. immigration authorities are barring entry to a 21-year-old Syrian cinematographer who worked on a harrowing film about his nation's civil war, "The White Helmets," that has been nominated for an Academy Award.

According to internal Trump administration correspondence seen by The Associated Press, the Department of Homeland Security has decided at the last minute to block Khaled Khateeb from traveling to Los Angeles for the Oscars.

Khateeb was scheduled to arrive Saturday in Los Angeles on a Turkish Airlines flight departing from Istanbul. But his plans have been upended after U.S. officials reported finding "derogatory information" regarding Khateeb.

Derogatory information is a broad category that can include anything from terror connections to passport irregularities. Asked for comment, a spokeswoman for the Department of Homeland Security, Gillian Christensen, said, "A valid travel document is required for travel to the United States."

"The White Helmets," a 40-minute Netflix documentary, has been nominated for Best Documentary Short. If the film wins the Oscar, the award would go to director Orlando von Einsiedel and producer Joanna Natasegara. Khateeb is one of three people credited for cinematography; Franklin Dow is the film's director of photography.

The film focuses on the rescue workers who risk their lives to save Syrians affected by civil war. Many of the group's members have been killed by Syrian President Bashar Assad's air forces. The group was nominated for last year's Nobel Peace Prize.

"The White Helmets" includes emblematic scenes of the deadly 6-year-old conflict: people digging through destroyed homes looking for survivors, at constant risk of "double tap" attacks that target first responders after they've arrived at the scene of a strike.

Khateeb had been issued a visa to attend the ceremony with Hollywood's biggest stars. But Turkish authorities detained him this week, according to the internal U.S. government correspondence, and he suddenly needed a passport waiver from the United States to enter the country.

Reached by telephone, Khateeb said he was currently in Istanbul and had not been detained. He declined to speak further about his situation. And a posting on the White Helmets' Twitter account said that "sadly," Khateen would not be able to attend the Oscars. "Not allowed to leave Turkey because passport not issued by Damascus," according to the tweet.

The correspondence indicated he would not receive such a waiver. There was no explanation in the correspondence for why Turkey detained Khateeb.